The present invention relates to a current-detecting resistor for use in a power converting apparatus such as an inverter.
In a power converting apparatus such as an inverter or a power module mounting thereon an IGBT device or the like, there is provided a high accuracy resistor of about 0.1 to 100 mxcexa9 so as to accurately detect a heavy current of between several A and 400 A. The power converting apparatus must radiate since the resistor generates a large amount of power due to the heavy current. As a means for radiation, a resistor is used which is constructed by laminating a resistance alloy plate 2 and a radiating metallic plate 4 via a resin insulating layer 3 as shown in FIG. 1. Such a resistor comprised of laminated three layers is disclosed in Japanese Patent Publication No. 3-16799 and Japanese Patent Laid-Open Publication No. 10-149901.
A copper manganese alloy, a copper manganese nickel alloy, or a copper nickel alloy having a high resistivity is used as a resistance alloy in order to detect electric current with a high accuracy. A manganin is known as an example of the copper manganese nickel alloy. Trade names such as Advance or Ideal containing a small amount of Mn, Fe and Si as well as a constantan are known as examples of the copper nickel alloy.
The above-mentioned laminated resistor, however, has several problems that will be discussed in greater detail.
FIG. 2 shows the temperature coefficient of resistance at the respective temperatures of a manganin (containing 85% copper, 12% manganese, 2% nickel, and 1% iron) as a typical copper manganese nickel alloy, and the copper nickel alloy (containing 54.5% copper, 43.7% nickel and 1.8% manganese). In the case of the copper manganese alloy or the copper manganese nickel alloy that has been in a relatively wide use, the absolute value of the temperature coefficient of resistance is as extremely small as 10 ppm/xc2x0 C. or less if the ambient temperature lies inside a range of a normal temperature to 60xc2x0 C., but is increased as the ambient temperature is raised or lowered to go out of this range. To the contrary, in the case of the copper nickel alloy, the absolute value of the temperature coefficient of resistance is constant at 15 ppm/xc2x0 C. or less irrespective of the ambient temperature. Therefore, the power converting apparatus whose ambient temperature is increased to 100xc2x0 C. requires the use of the copper nickel alloy that exhibits a small temperature coefficient of resistance when the peripheral temperature is high.
Joule""s heat is generated in the resistance alloy plate 2 when carrying current. In order to correctly measure the current, the resistor for use in the power converting apparatus must control the rise in the temperature of the resistance alloy plate 2 so as to prevent the temperature of atmosphere inside the power converting apparatus from rising due to the generated heat. The laminated resistor radiates and cools the generated heat through the resin insulating layer 3. Accordingly, the heat conductivity of the resin insulating layer 3 is desired to be as high as possible.
Adding a larger amount of inorganic filler material is more advantageous in increasing the heat conductivity. The amount of inorganic filler material added to resin material for the conventional laminated resistor is 70 wt % at the most, and the resistor has a low heat conductivity and a high heat resistance. Therefore, the cooling property is not satisfactory. If a heavily-filled resin material with inorganic filler material of 80 to 90 wt % added thereto in order to improve the radiating property, the contact surface area between the filler material and the metallic surface is decreased to deteriorate the adhesiveness with respect to the resistance alloy plate 2. To improve the adhesiveness, the adhesion surface is usually roughened. An electrolytic copper foil or the like for use in a printed circuit board is roughened over a depth of 5 to 15 xcexcm. Even a heavily-filled resin material with inorganic filler material of 80 to 90 wt % being added thereto has as a strong anchoring effect. In the case of a rolled copper foil having a smooth surface, a needle crystal of oxidized copper is grown on the surface to toughen the surface in a so-called blackening process. Recently, the surface of copper has been roughened over a depth of several xcexcm in a so-called micro-etching process.
A rolled plate serving as the resistance alloy plate 2 for use in conventional laminated resistors has a smooth surface. For this reason, the surface cannot be roughened unless the roughing process is carried out, as is the case with a rolled foil. As is the case with the rolled copper foil, the above-mentioned copper manganese alloy or copper manganese nickel alloy can easily be blackened or micro-etched since it contains a large amount of copper; 82 to 85%. To the contrary, the copper nickel alloy whose temperature coefficient of resistance is constant at a low level in a wide temperature range is essentially difficult to oxidize, and it is therefore difficult to roughen the copper nickel alloy like the copper manganese alloy or the copper manganese nickel alloy.
If the resistor is mounted directly on a metallic plate of a power module with an earthing potential to enable efficient cooling, the circuit voltage of the power converting apparatus is applied to the insulating resin layer 3. The applied circuit voltage may reach about 1000 Vp (peak voltage) at the most. Accordingly, the insulating resin layer 3 needs to have a high dielectric strength and maintain it for a long period of time.
In view of the above, it would be desirable to provide a resistor for use in a power converting apparatus, which is capable of achieving a high adhesive strength between a resistance copper nickel alloy plate and a heat conductive resin material, a low heat resistivity, an excellent cooling property, and an excellent insulating property.
It would further be desirable to provide a resistor for use in a power converting apparatus, which is capable of achieving a small temperature coefficient of resistance within a wide temperature range, a high accuracy in current detection, a high adhesive strength between a resistance plate and a heat conductive resin material, a high heat conductivity, an excellent cooling property, and an excellent insulating property.
A resistor is provided wherein an electrical resistance alloy plate and a radiating metallic plate are laminated via a resin insulating layer 3, the electrical resistance alloy plate is formed of an alloy containing nickel of 42.0 to 48.0 wt %, manganese of 0.3 to 2.5 wt %, and copper on the basis of the total weight of the alloy with the total content of copper, nickel and manganese being not less than 98 wt %, and has a thickness of 1 mm or more, and a grain boundary thereof is etched in the form of a concave so that the electrical resistance alloy plate can be adhered to the resin insulating layer.